Sound recorder and reproducer



Feb. 12, 1935. c KELLER 1- 1,990,548

SOUND RECORDER AND REPRODUCER Filed June 20, 1934 A. C. KELLER INVENTORSI. S RAFUSE A TTORNEV Patented Feb. 12, 1935 UNITED STATES PATE SOUNDRECORDER AND BEPRODUCER Arthur C. Keller, Mount Vernon, and Irad S.Rafuse, Hempstead, N. Y., assignors to Bell Telephone Laboratories,

Incorporated, New

larly since the advent of electrical recorders, to

use a so-called advance ball to regulate the depth of the groove beingcut. The advance ball is usually in the form of a jewel cylinder mountedon the recorder near the stylus and having a spherically ground endwhich slides over the uncut portion of the wax surface.

The reproduction of phonograph records is accompanied by more or lessextraneous noise. Some of this noise originates in the recording itself,some of it is added in the duplicating process, and some of it is due tothe nature of the material from which the pressings are made.

elimination of this noise and recent developments have so greatlyreduced the noise due to other causes that the mechanical disturbancescaused by the advance ball as it slides over the wax are now audible infinished records and are often predominant in original recordings.

Noise of this latter type is eliminated according to the invention bykeeping the recorder in proper position with respect tothe recordingsurface by means of a stable system of forces set up by an expandingfluid stream flowing between the recorder and the recording surface. Thepreferred structure comprises a tube leading from'a source of compressedand preferably flange on the recorder adjacent the stylus and 'justabove the recording surface. The impact of the air moving downwardlytends to raise the flange above the surface and the increasingcross-section of the air path as the air moves radially outward alongthe flange produces an area of less than atmospheric pressure under theflange which tends to keep the flange near the recording surface. Forany given recorder structure and suitable air pressure applied to thetube, the flange, under the action of these opposing forces, takes aposition slightly above the surface and supports the recorder in stableequilibrium without any mechanical contact with the moving recordsurface. This supporting structure does not disfigure the recordingsurface even when the wax used would be entirely too soft to-permit theuse of a conventional advance ball, and it has the further advantagethat any tendency of the recorder Considerable progress has been madetoward the filtered air and terminating in a relatively largeto bounceas when accidentally jarred is' very quickly suppressed. The recorderitself may be made much heavier and more rugged than when an advanceball is used, so that the reactions of the record material on thecutting 5 stylus do not affect the shape of the groove being cut.

The flange is usually flat but in some cases it may be in the form of aspherical segment, as explained more fully below. When the flange ismounted near the stylus, the force of the air on the vibrating stylusmay produce a slight undesirable disturbance. This is prevented,according to the invention, by means of an air trap in the flange on theside nearest the stylus for reducing the flow of air at this point.

In most reproducing systems the reproducer functions satisfactorily withthe unbalanced weight of the reproducer supported by the stylus, but incertain special cases, the present 20 invention may also be used toadvantage with reproducers. When used for example with a reproducerwhich tends to jump into an adjacent groove due to the large amplitudeof groove undulations or for other reasons, the partial 25 vacuumdeveloped under the flange is very efiective in keeping the stylus incontinuous contact with the groove. When the invention is applied toplayback devices for reproducing original recordings, the vibratorystructure may be much 9 more fragile than in cases where the stylussupports the unbalanced weight. This makes it possible to reduce theweight of the playback and the mechanical impedence of its moving systemto such low values that even. very soft 35 records can be reproducedwithout injury to the grooves.

These and other features of the invention will be more fully understoodfrom the following detail description and the accompanying draw- 40 ing,in which Fig. 1 shows a conventional electrical recorder supported incutting position according to this invention;

Figs. 2 and 3 are enlarged views of the recorder and its air tubesupporting structure; 7

Fig. 4 is a terminating flange with one form of air trap;

'Fig. 5 is an eccentric flange for diverting the 'air from the stylus;

Fig. 6 is an air tube with a spherical instead of a flat flange; and

Fig. '7 is a bottom view of a translating device with the flange infront of the stylus.

Referring now to Figs. 1, 2 and 3. the trans- 5 lating device 11 shownfor the purpose of illustrating the invention is a recorder of a timenow in general use which is ordinarily partially balanced about itshorizontal pivot 12 by a counterweight (not shown), the unbalanced massbeing supported by an advance ball near the stylus 13. In this case theadvance ball is replaced by the pneumatic system of this inventioncomprising the-tube or air conduit 14 which is connected to the tank 15of compressed air by the flexible tubing 16.

Since dust and moisture would impair the record surface, suitablefiltering apparatus 29 is connected in the supply line and a pressurereducing control valve 17 is provided to regulate the air pressure inthe tube 14. The ratio of the flangediameter to the bore of the tube isnot very critical and depending von the particular structure to besupported it may vary from about 2 to 1 to something less than 10 to 1.In the structure of Figs. 2 and 3, the tube is of one eighth inch boreand terminates in a flat flange 18 about one half inch in diameter. Bymeans of the valve 1'7, air is applied to the tube at five to fifteenpounds gauge pressure and the recorder may then be safely placed on therotating record blank 22. As the flange approaches the record surface,the escaping air is deflected and moves radially outward between theopposed surfaces as indicated by the arrows in Fig. 1 and a position ofequilibrium is reached with the flange about two or three mils above thewax surface 22.

Some physio text-books describe an experiment illustrating thisphenomenon in which a sheet of paper is held from falling away from thebottom of a spool by blowing downwardly through the hole in the spool.Applicants structure just described, however, supports a recorder inproper cutting position with a surprising degree of stability. Adownward blow on the recorder much more severe than any disturbancelikely to arise inadvertently during the making of a record producesonly a momentary and almost imperceptible decrease in the spacingbetween the flange and the wax and the low pressure area under theflange makes it necessary to apply a force of about 100 grams to liftthe recorder from the wax.

Since the recording surface cannot readily be made optically flat, it isdesirable to mount the flange as near to the stylus as possible so thatthe flange will follow irregularities 'in the wax surface and therebymaintain the stylus at the proper cutting depth. For the recorder ofFig. 2, it is most convenient to mount the flanged tube on the side ofthe recorder as shown. While the depth of out can be regulated to someextent at least by varying the air pressure, it is desirable to providea mechanical adjustment for the tube 14. In the form illustrated thetube is a sliding fit in the bracket 23 and is held in verticaladjustment by the clamping member 24. The adjusting screw 25 ispreferably of the compound type having an upper threaded portionengaging the member 24 and a lower portion with threads of slightlydifferent pitch engaging the bracket 23. If, for example, the threadsused are thirty-six and forty per inch, respectively, a quarter turn ofthe screw will change the depth of the groove cut by less than threequarters of a mil-inch and obviously by resorting to special threads anydesired degree of fineness of adjustment may be obtained. In practice arecorder is usually adjusted with great care by a skilled operator, butin somecases it may be positioned with the flange at a slight angle tothe wax surface. If in such a case the tube 14 is made in two sectionsconnected by a rubber or other flexible coupling 26 as shown in Fig. 6,a greater flow of air occurs on the side of greatest spacing producing agreater downward force in this region and the flexible coupling permitsthe flange to take up its proper position parallel to the wax surface.The flexible connection obviously may also be used with air conduitshaving flanges of the types shown in Figs. 4 and 5.

Since there is no mechanical contact with the wax, no noise of the typeproduced by a sliding advance ball is introduced into the record. Theold type advance ball was also objectionable in that it slightly smearedthe wax surface and since the ball preceded the stylus this disfiguringspiral was often quite noticeable in finished pressings at the end ofthe record groove. With the pneumatic tube of this invention nodisfiguration occurs and the flange may either precede or follow thestylus across the record so that the recorder may be used without changeto cut grooves either toward or away from the center of the record.

It has already been explained that the flange should be mounted asclosely as possible to the cutting stylus but when a simple flange ofthe type shownin Fig. 1 is used the pressure of the escaping air on thestylus may produce a slight modulating or distorting effect on itsvibrations and a corresponding characteristic noise is heard when therecord is reproduced. When it is impractical to make the vibratingstructure rigid enough to eliminate this effect entirely, thisdistortion may be prevented by stopping or diminishing the air flow inthe direction of the stylus. In the preferred structure foraccomplishing this result as shown in Fig. 2, the flange is providedwith a segment of about ninety degrees (Fig. 4) extending beyond thecircular portion and containing a deep circumferential groove 19, theouter rim 20. of the segment being coplanar with the face 21 of theflange or extending about one mil below the flange. The acousticimpedance along the groove 19 is very low compared to the impedancebetween the rim 20 and the waxso that most of the air moving radiallytoward the stylus will be deflected tangentially and the modulatingeffect on the stylus is substantially eliminated. Alternatively theflange itself may be eccentric with respect to the air conduit toprovide a longer acoustic path and hence one of higher impedance in thedirection of the stylus. One such flange is illustrated in Fig. in whichthe air path from the end of the conduit 2'7 to the outer rim at 28 istwo or three times aalong as the path in the opposite direction. It willbe understood that the configuration ofsuch a flange may be variedconsiderably to obtain the efiect desired in a particular case.

When the design of the recorder or reproducer permits or when it hasbeen specifically designed with this in view, it is of some advantage tolocate the flange 18 in front of the stylus 13 as shown in the bottomview of a recorder in Fig. '7. With this arrangement the translatingdevice is equally well adapted to move across'a record either from theoutside in or from the inside out since the small blank space ordinarilyleft beyond the outer groove is of suflicient width to prevent the airfrom escaping freely from the tube when the recorder or reproducer isnear the periphery of the record.

In the foregoing description the several flanges discussed are flat butif desired a spherical flange with a radiusof curvature of the order ofsix to twelve inches as shown in Fig. 6 may be used. It will also beunderstood that the curved flange maybe provided with any suitable formof air trap for deflecting the air from the stylus.

While the invention has been described with reference to a system usingcompressed air to support the recorder, it will be understood that anyother gas or liquids such as water may be used if desired. For examplewhen the record blank is submerged in water during the cutting operationto prevent dust from accumulating'in' the groove, it may be advantageousto use water instead of air as the supporting fluid.

What is claimed is:

1. The combination with a record member and a vibration translatingdevice cooperating therewith, of a fluid conduit on the device having aflange member in close spaced relation to the record member, and meansfor producing a flow of fluid between said members for maintaining thespacing between them.

2. The combination with a. record member and a pivoted recording devicefor,forming a groove in -the member of means for maintaining a desiredspacing between the member and the device comprising a conduit for afluid stream on the device terminating at one end in a flange close tothe surface of the record member, and a source of fluid under pressureattached to the other end of the conduit.

3. The combination with a record member and a vibration translatingdevice cooperating therewith of means for maintaing a desired spacingbetween the device and the surface of the member comprising an annularsurface on the device in close spaced relation to the surface of themember, and means for producing an'outward radial flow of fluid betweenthe surfaces.

4. The combination with a record member and a vibration translatingdevice having a stylus cooperating with the member, of a tube on saiddevice connected to a source of fluid under pressure and terminating ina flange substantially parallel to the record member, and means forreducing the flow of fluid in the direction of the stylus.

5. The combination with a record member and a translating device havinga stylus cooperating with the member, of a conduit for a fluid streamattached to the device, a flange in close spaced relation to the membernear the stylus mounted on the conduit, and a protruding segment on theflange having a groove therein for deflecting the fluid away from thestylus.

6. The combination with a record memberand a translating device having astylus cooperating with the member, of a conduit for a fluid streamattached to the device, and a flange in close spaced relation to themember near the stylus eccentrically mounted on the conduit; Y

7. The combination with a record member and a translating device havinga stylus cooperating with the member, of a conduit for a fluid streamattached to the device, a flange in close spaced relation to the member,and a flexible connection between the flange and the conduit.

8. The combination with a record blank and a recorder having a stylusfor forming a groove in the blank, of a conduit for a fluid streamattached to the recorder, a flange on the conduit in close spacedrelation to the blank near the stylus, means for supplying fluid underpressure to the conduit, and means for varying the spacing between theflange and the record blank.

9. The combination with a record member and a translating device havinga stylus cooperating with the member, of means for maintaining thedevice in operative relation to the member comprising a source of fluidunder pressure, a conduit for a fluid stream from said source attachedto the device, and a flange on the conduit in close spaced relation tothe member above the groove engaged by the stylus.

' ARTHUR C. KELLER.

lRAD S. RAFUSE.

